如何向绑定到实体的组合框中添加新项

本文关键字：组合 添加 新项 实体 绑定 | 更新日期: 2023-09-27 18:10:28

c#生成的设计类:

    // 
    // usepurposeComboBox
    // 
    this.usepurposeComboBox.DataSource = this.usepurposeBindingSource;
    this.usepurposeComboBox.DisplayMember = "Name";
    this.usepurposeComboBox.FormattingEnabled = true;
    this.usepurposeComboBox.Location = new System.Drawing.Point(277, 53);
    this.usepurposeComboBox.Name = "usepurposeComboBox";
    this.usepurposeComboBox.Size = new System.Drawing.Size(218, 21);
    this.usepurposeComboBox.TabIndex = 4;
    this.usepurposeComboBox.ValueMember = "id";
    // 
    // usepurposeBindingSource
    // 
    this.usepurposeBindingSource.DataSource = typeof(mydatabaseEntities.usepurpose);

然后我将BindingSource (usepurposeBindingSource)绑定到Entities:

usepurposeBindingSource.DataSource = mydatabaseEntities.usepurposes;

我不能给usepurposeComboBox添加新行因为它被绑定了。

如何向绑定到实体的组合框中添加新项

最简单的方法是在dataTable中添加一个新行，然后将comboBox绑定到它，就像这样:

Company comps = new Company();

        //pupulate dataTable with data
        DataTable DT = comps.getCompaniesList();
        //create a new row
        DataRow DR = DT.NewRow();
        DR["c_ID"] = 0;
        DR["name"] = "Add new Company";
        DR["country"] = "IR";
        //add new row to data table
        DT.Rows.Add(DR);
        //Binding DataTable to cxbxCompany
        cxbxCompany.DataSource = DT;
        cxbxCompany.DisplayMember = "name";
        cxbxCompany.ValueMember = "c_ID";

我假设你想添加例如第一个项目有时称为"Choose One"，如果你想要实时数据，你应该看看数据来自哪里，并添加更多的项目到那个"表"。

this.usepurposeBindingSource是一个对象…为什么不在它结合之前加入呢?

如果是List<T>就可以

this.usepurposeBindingSource.Insert(0, new T() {
    Name = "Choose one",
    Id = ""
});

Then Bind() it…

记住要验证，因为它是一个字符串，而不是你想要的对象

正在运行:

List<MyObject> usepurposeBindingSource { get; set; }
private void FillUpData()
{
    // Simulating an External Data
    if (usepurposeBindingSource == null || usepurposeBindingSource.Count == 0)
    {
        this.usepurposeBindingSource = new List<MyObject>();
        this.usepurposeBindingSource.Add(new MyObject() { Name = "A", ID = 1 });
        this.usepurposeBindingSource.Add(new MyObject() { Name = "B", ID = 2 });
        this.usepurposeBindingSource.Add(new MyObject() { Name = "C", ID = 3 });
    }
}
private void FillUpCombo()
{
    FillUpData();
    // what you have from design
    // comment out the first line
    //this.usepurposeComboBox.DataSource = this.usepurposeBindingSource;
    this.usepurposeComboBox.DisplayMember = "Name";
    this.usepurposeComboBox.FormattingEnabled = true;
    this.usepurposeComboBox.Location = new System.Drawing.Point(277, 53);
    this.usepurposeComboBox.Name = "usepurposeComboBox";
    this.usepurposeComboBox.Size = new System.Drawing.Size(218, 21);
    this.usepurposeComboBox.TabIndex = 4;
    this.usepurposeComboBox.ValueMember = "id";
    // to do in code:
    this.usepurposeBindingSource.Insert(0, new MyObject() { Name = "Choose One", ID = 0 });
    // bind the data source
    this.usepurposeComboBox.DataSource = this.usepurposeBindingSource;
}

技巧是注释掉DataSource行，并在您的代码中执行，插入一个元素到您的对象中，该对象来自您的模型

//this.usepurposeComboBox.DataSource = this.usepurposeBindingSource;

最简单的方法是用某种"ViewModel"来包装你的BindingSource。新类将返回一个"完整"的项列表——既包括原始绑定源提供的项，也包括那些"附加"项。

然后可以将新的包装器绑定到组合框。

我之前写过一篇关于这个的文章…这不是我最好的作品，而且可能有点过时了，但它应该能让你达到目的。

我自己解决了。我创建了一个新的未绑定组合框，然后将其绑定到一个数据表。我不确定这是不是最好的方法，但对我来说很有效。谢谢你的建议。:) 

private void FillCombobox()
        {
            using (mydatabaseEntities mydatabaseEntities = new mydatabaseEntities())
            {
                List<usepurpose> usepurposes = mydatabaseEntities.usepurposes.ToList();              
                DataTable dt = new DataTable();
                dt.Columns.Add("id");
                dt.Columns.Add("Name");
                dt.Rows.Add(-1, "test row");
                foreach (usepurpose usepurpose in usepurposes)
                {
                    dt.Rows.Add(usepurpose.id, usepurpose.Name);
                }
                usepurposeComboBox.ValueMember = dt.Columns[0].ColumnName;
                usepurposeComboBox.DisplayMember = dt.Columns[1].ColumnName;
                usepurposeComboBox.DataSource = dt;
            }
        }

查看此链接:http://forums.asp.net/t/1695728.aspx/1?

在asp中，你可以添加这个来插入一个空行:

    <asp:DropDownList ID="CustomerDropDownList" runat="server"
    DataSourceID="CustomerEntityDataSource" DataTextField="CustomerId"
    DataValueField="CustomerId" AppendDataBoundItems="true">
    <asp:ListItem Text="Select All Customers" Value="" />
    </asp:DropDownList>

或在代码后面:

    DropDownList1.AppendDataBoundItems = true;
    DropDownList1.Items.Add(new ListItem("Select All Customers", "-1"));
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